Ultrasonic skis or the like

ABSTRACT

An object supporting system in the form of a ski adapted to transmit ultrasonic mechanical vibrations so as to quantitatively reduce the frictional sliding engagement between the skis of the user and the support surface.

United States Patent 1191 Suroff 1 Nov. 27, 1973 [54] ULTRASONIC SKIS OR THE LIKE 3,073,219 1/1963 Miller 94/48 3,233,363 2/1966 Maury.... 273/86 E X [76] Invent: Lm'md Sum, 12 Tompkms 3,251,607 5/1966 Wren 280/11.37 E x N Jeflcho, 11753 3,628,789 12/1971 Suroff 272/56.5 ss [22] Filed: Dec. 15, 1971 PP 208,326 Primary Examiner- Kenneth H. Betts Related s Application D Assistant Examiner-David M. Mitchell [63] Continuation-impart of Ser. No. 804,451, March 5,

1969, Pat. No. 3,628,789.

52 us. (:1. 280/11.l3 R, 272/565 ss [571 ABSTRACT [51] Int. Cl A63c 5/00 [58] Field of Search 272/565 SS, 86 E; An object supporting system in the form of a ski 180/1 AV, 125; 280/11.13 R, 11.13 M.11.37 adapted to transmit ultrasonic mechanical vibrations E, 11.13 F; 94/50 Y, 48 so as to quantitatively reduce the frictional sliding engagement between the skis of the: user and the support [5 6] References Cited surface.

UNITED STATES PATENTS 2,639,777 5/1953 Dull 180/1 AV 32 Claims, 4 Drawing Figures ULTRASONIC SKIS OR THE LIKE CROSS-REFERENCE TO RELATED APPLICATIONS BACKGROUND OF THE INVENTION This invention relates to skis to provide a minimum of frictional interference and more particularly is concemed with the method and apparatus for providing skis having an ultrasonically vibrated surface for substantially reducing the frictional sliding engagement between the skis and ski-slope.

The present invention is applicable to the use of skis which speed of movement is related to the degree of friction between the ski and support surface, and which frictional resistance is reduced by ultrasonically vibrating the ski. The invention is applicable to skis, ice skates, snow skis, water skis, tobaggan, etc., and since this invention is ideally suited for use with skis it will be so illustrated and described.

OBJECT OF THE INVENTION It is therefor an object of the invention to provide an improved method and apparatus for producing a surface adapted to be ultrasonically vibrated to obtain substantial friction reduction between the object and the support surface.

Another objectof the invention is to provide skis vibrated at an ultrasonic rate with a small amplitude of vibration in the direction perpendicular to the bottom surface of the ski so that the vibrations quantitatively reduce the frictional resistance of the skis relative to the support surface.

Another object of the invention is to provide a ski in which the coefficient of friction between skis and the support surface may be varied depending on the desire of the skier or weather.

Other objects and advantages of the invention will be apparent as the disclosure proceeds.

SUMMARY OF THE INVENTION ultrasonic rate, with the term ultrasonic" defined to include vibrations in the range of 10,000 to 1,000,000 cycles per second.

The present invention permits an individual to ski down a slope with skis on without the necessity of having snow or some other artificial medium thereon. This immediately permits an individual in warm weather to utilize artificial ski-slopes that have heretofore had to rely on man made or natural snow. By providing a ski that is ultrasonically vibrated the degree of friction reduction can be controlled by varying the amplitude and/or frequency of vibration.

Accordingly, when the ski is ultrasonically vibrated at least in a plane perpendicular to the static pressure of the user so that relative movement or displacement between skier and ski-slope is affected in the direction of the slope so that the anti-friction effect of the vibrations of the ski are relied upon to permit the free niovement of the skis relative to the ski support surface in the direction of the slope.

In accordance with the present invention a ski is utilized that may have plurality of zones of vibratory motion such that the skier is always suspended on at least two zones of vibratory motion. By being able to control the amplitude and frequency of vibration, it is possible to properly monitor same such that depending upon the degree of competence of the individual he might if he so desired for his ski run, preselect the degree of friction reduction that suits his needs. For example, the skis can be made as fast as if it was pure ice or if were essentially earth such that between the two the degree of friction may be selected.

Each ski may be made to vibrate at a number of locations along the bottom ski by coupling one or more transducers thereto, thereby ensuring that a plurality of zones or points along the desired ski will have elastic vibratory energy introduced therein so that the ski support surface is always in contact with substantially two vibratory zones.

In accordance with an aspect of the present invention, the ski is vibrated so that the ultrasonic energy may be applied thereto and have a component of vibration at the bottom surface, and the vibratory energy of the present invention may be so directed as to simultaneously provide components of motion both in the shear mode and perpendicular to the ski surface. The two directional motion may result from generating an orbital vibration at the contact edge of the vibratory element.

In accordance with another aspect of the invention, the vibrations are applied to the ski and the high frequency and amplitude of the vibrations are selected so as to achieve large peak accelerations, for example, accelerations of the order of at least 1,000 g. g being the symbol representing gravitational acceleration, whereby a relatively small static force in the direction of the slope by the skier produces relatively large dynamic forces between the skis and the ski support surface to effect the desired relative movement therebetween.

In accordance with another aspect of the invention the ski has a plurality of transducers or motors coupled thereto in spaced apart relationship a given distance apart, which distance is less than the distance of the length of the skis.

BRIEF DESCRIPTION OF THE DRAWINGS Although the characteristic features of this invention will be particularly pointed out in the claims, the invention itself, and the manner in which it may be made and used, may be better understood by referring to the following description taken in connection with the accompanying drawings forming a part hereof, wherein like reference numerals refer to like parts throughtout the several view and in which:

FIG. 1 is a diagrammatic view in perspective of a ski slope with a skier having ultrasonic skis according to the present invention;

FIG. 2 is a greatly enlarged end view illustrating the motion of the vibratory surface at the bottom of the skis shown in FIG. 1, to aid in explaining the reduction of friction concept;

FIG. 3 is a diagrammatic view which illustrates an al ternate form of ski having the ultrasonic vibratory means associated therewith in accordance with the invention; and

FIG. 4 is a greatly enlarged view in section of the embodiment in FIG. 3.

PREFERRED EMBODIMENTS OF THE INVENTION Referring to the drawings in detail and initially to FIGS. 1 and 2 thereof, it will be seen that an object supporting system in the form of an ultrasonic ski-slope embodying the present invention is generally identified by the reference numeral 10, and includes supporting means 12 having a ski support surface means 14 on which the skier 15 can ski with skis 16 contacting the ski support surface 14 which is sloped downwardly at any desired angle as well as curvature. The ski support surface 14 may be formed from one or a plurality of individual support members 18 in the form of sheets or panels extending from several feet to several thousand feet in length and having a width which is convenient to transport, as for example, 4 to 50 feet in width. The support member 18 is formed out of material capable of supporting ultrasonically vibrating skis 16, which is preferably metallic, plastic or some composite or laminate material. The skis of the present invention can also be used on snow. The support member is relatively thin as compared to its width or length and defines a planar ski support surface 14 which may be of a thickness in the range of 0.0l0.10 inches. The support members 18 may be supported on the ground or by vertically extending support beams 20 used in spaced apart relation to each other as part of the supporting means 12.

To produce the friction reduction effect ultrasonic vibration generating means 22 is utilized and is coupled to the skis 16 so as to apply ultrasonic energy to the bottom or contacting surface 36 to produce mechanical vibrations having a component substantially normal to the bottom surface 36 so that the coefficient of fl'iCr tion between the ski support surface 14 and skis 16 is substantially reduced to permit skiing thereon. The vibration may be continuous to vibrate the entire ski surface 36 in phase, or due to the size of the surface zones of vibratory motion 25 may be produced either in a predetermined spacing or by random vibration. Accordingly, the generator means 26 may be of the type known in the art and adapted to continuously vary the frequency of vibration of the transducer or ultrasonic motor 28 so as to vary the position of the zones 25 of vibration along the surface 36 at any location thereon. Accordingly, there is produced by means of mechanical vibratory energy zones of vibration at the bottom surface 36 of the skis 16; these zones of vibration may be proximate to a related ultrasonic motor 28 and having a certain spacing between the respective zones of vibration which may be created due to the spaced apart relationship of the respective motors 28 or, if the frequency of vibration of the ultrasonic motor 28 is varied, then by random selection there is in effect a continuous sweep across the surface 36 of the skis whereby the zones of motion are continuously changing under a predefined pattern if so desired.

Accordingly, the vibration generating means 22 includes a vibration generator 26, which may be of an adjustable type to vary frequency by control knob 29 and power to vary amplitude by control knob 30, and one or more ultrasonic motors or transducers 28 coupled to the upper surface 17 of the skis 16 so as to generate ultrasonic mechanical vibrations, and connected by cables 34 to the generator 26. The generating means 22 may be battery powered and secured to the back of the skier 15 such that he or she merely places it on when getting dressed. The battery may be of the rechargeable type such that overnight the battery may be recharged for use from day to day. The cables 34 may be held in place by snaps on the garments of the skier 15. The transducer 28 may be one of a number of electromechanical types, such as, electrodynamic, piezoelectric or magnetostrictive, however, for the operating range of frequencies most desirable for an ultrasonic ski 16 the transducer 28 is preferably of the piezoelectric type. The transducer 28 is preferably formed of a crystal material well known in the art, so that the transducer will vibrate to a maximum degree when subjected to the influence of an electric current supplied from the oscillation generator 26. The transducers 28 produce ultrasonic vibration which effects elastic vibration of the ski surface 36, at a high frequency of at least 10,000 cycles per second with peak accelerations of the order of at least 1,000 g, whereby the frictional resistance of the skis 16 to the support surface 14 is quantitatively reduced so that the force to permit skiing may be of a relatively small magnitude.

By coupling one or more transducers 28 to the top 17 of the ski 16 the plurality of zones 25 of vibratory motion may be obtained on the ski bottom 36, with the spacing of the zones 25 being such that each ski 16 is substantially always in supporting relationship to at least two zones of vibratory motion. It is possible to vibrate the entire ski surface 36 in a certain phase relationship, but to be economical with respect to the power required it is deemed desirable that as long as there are sufficient number of zones of motion, having a component in the plane normal to the direction of movement the skier 15, that the friction reduction effect will be sufficient to permit him to propel himself downward at a rapid speed on a metallic or other surface.

The magnitude of friction reduction is in part related to the actual amplitude of vibration as seen in FIG. 2, in that the ski surface 36 is moving from between the solid line, at the end of a vibratory cycle, to the phantom surface line at the other end of the vibratory cycle, approximately 20,000 cycles per second, at say an amplitude of vibration of 0.002 inch, which essentially means that it is continuously moving away from the surface 14 of the ski support 12 at a quicker rate than the gravitational force of gravity such that in a sense only upon the ski surface 36 reaching its peak height is it momentarily in contact with the surface 14 of the ski support 12. This phenomenon is a unique property of ultrasonic vibratory mechanical energy which can be utilized in a ski so as to permit one to ski down with a minimum of resistance. Controlling the coefficient of friction between the object in the form of skis l6 and ski-slope 10 is obtained by varying the amplitude and- /or frequency of vibration which makes it possible to control the degree of friction reduction, which is controllable by the individual or operator of the skis. This control is obtained by adjusting the knob 29 and/or knob 30.

It has been found that, by reason of the vibrations in a plane perpendicular to the direction of the static force, the frictional resistance of the skis 16 to movement on the ski-slope 10 is very substantially reduced.

A possible explanation of this observed phenomenon is that the extremely high acceleration of the bottom surface of the ski surface 36 resulting from the vibrations causes only a relatively small sliding friction to be present betweenthe engaged ski 16 and the surface 14. Thus,even though the ski support surface 14 is stationary and may have a flat surface, the skis 16 are nevertheless easily displaceable with respect thereto, for example, in the direction of the slope on FIG. 1, thereby to easily move down the slope.

The static pressure or force exerted on the ski sup port surface 14 maybe in the range of between approximately 50 to 5,000 pounds in a given area, such as by one or more skiers or a snow mobile or toboggan. As illustrated in FIG. 2, the frequency of the vibrations between the solid and phantom line at a zone 25 at the free end portion of the ski surface 36 may be in the rangefrom to 100 kilocycles per second and preferably in the range from 20 to 80 kilocycles per second, while the amplitude of the vibrations is selected within the range from approximately 0.0005 to 0.025 inch so as to ensure the introduction of vibratoryenergy sufficient to substantially minimize the frictional resistance of the support surface 14 to the advancement of the skiis16. It being appreciated that one or more skiers 15 .may be simultaneously using the ski-slope 10.

The ski surface 36 may vibrate at 20,000 cycles per second a distance longitudinally approximately 0.002 inch, or say in the range of 0.002-0.003 inches. This vibration achieves peak acceleration of about 41 ,000-62,000g and forms the zone of motion" which is essentially impenetrable by the moving object. The actual contact of the ski 16 with the surface 14 is for only a small portion of each cycle of vibration such that the object actually rides on a cushion of air and friction is therefore reduced to almost zero.

Accordingly, suppose the ski surface 36 has a peak stroke of 0.004 inch, then it would reach the peak acceleration of 82,000g. So, in the first instance we see that the output is relatively low speed 21 ft./sec. which is approximately 14 miles/hour. But the peak acceleration exceeds anything that can be achieved in any other way by mechanical means at such low speed.

Therefore, one of our first discoveries about the vi brating surface is that its peak output speeds are very safe, while at the same time extraordinarily high accelerations are utilized. An immediate consequence of this fact is that for bodies moving with accelerations of say 1 g; i.e., the human body on the support surface, there will be very little penetration of the zone of motion. For example, suppose the skiis are in contact with the support surface 14 atthe end of a stroke and are capable of moving into the zone of motion with an acceleration of onevg. Then the ski surface 36 will retract a distance, S, and return the same distance in a time equal to one period of oscillation of the motor. Since, for 20,000Hz this period is 50 microseconds, we can calculate how fara l g. accelerated body, the skier 15, can move in 50 microseconds, starting from rest. This we get from the simple equation.

d=distance travelled a=acceleration due to gravity,

s=stroke d=0.483 X 10'' in.

F0004 in. 4 X 10 in.

d/s==0.0l2 X 10 or 0.012 percent Thus, d/s, which measures the penetration of the zone of motion amounts to less than 0.012 percent. Accordingly, the object; i.e., human, is moving toward the supporting surface with an acceleration of l g and the space penetration is less than 0.012 percent.

Thus, the object moving with such a vibrating surface would be in contact with the surface for less than 0.012 percent of the time. This means the ski 16 is essentially air-borne and so should exhibit practically no friction or no resistance to sliding along the surface 14.

Although the transducers 28 are shown physically to extend on top of the skis 16, it is appreciated that this is diagrammatic only and that the crystal transducers may be contained within the skiis. As is seen in FIGS.

3 and 4, the ski 16a is designed such that the transducer 28a is positioned in a cavity 40a contained therein and coupled to the cavity wall 42a such that the bottom surface 38a has the vibratory energy transmitted thereto. In this manner the transducer 28a need not be visible to the user. In addition, although the generator may be carried on the skier, it may be positioned on the ski 16a, or the ski 16a may be moved or formed having an enlarged portion 45a for the generator 26a. In any event the provision of the generator 26a and transducer 28a on each ski 16a permits each ski 16a to be positioned at night and have the battery associated therewith recharged via the electrical connector 46a shown positioned at the rear end of the ski 16a. The connector 46a, generator 26a and transducers 28a are electrically connected by cables 34a. The control knobs 29a and 30a may be depressed so when fixed in position the skier falling would not upset their position. Switches can be provided on the bottom surface so that if the skier falls the ultrasonic energy is automatically discontinued.

The upper surface 17a of the ski further includes retaining means in the form of say a front clip 48a and rear clip 50a to retain the boot 52a of the user 15a in fixed position relative thereto.

Although illustrative embodiments of the invention have been described in detail herein with reference to the accompanying drawing, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein wothout departing from the scope or spirit of the invention.

I claim:

1. The method of skiing on a ski supporting surface comprising the steps of A. providing a ski having a substantially continuous planar, bottom surface capable of transmitting ultrasonic vibrations and capable of supporting a skier wearing them,

B. coupling electromechanical vibratory mechanism means to said ski for transmitting mechanical vibrations on said ski bottom surface, and

C. activating said electromechanical vibratory mechanism means to produce said vibration at high frequency and low amplitude having a component substantially normal to said ski bottom surface, and with peak accelerations of the order of at least 1,000g, whereby the coefficient of friction between said ski bottom surface and the ski supporting surface is quantitatively reduced.

2. The method as defined in claim 1, wherein said ultrasonic vibration effects elastic vibration of said ski bottom surface at a frequency of at least 10,000 cycles per second.

3. The method as defined in claim 1, wherein said high frequency vibration is in the range of 10,000 to 1,000,000 cycles per second.

4. The method as defined in claim 1, and further including the step of controlling the coefficient of sliding friction between the ski and supporting surface by varying the amplitude of vibration of said ski bottom surface.

5. A method as defined in claim 1, and further including the step of controlling the coefficient of friction between the skis and ski-slope by varying the frequency of vibration of said ski bottom surface.

6. The method as defined in claim 1, wherein said vibration produces zones of vibratory motion along said bottom surface.

7. The method as defined in claim 6, wherein said zones of vibratory motion are randomly selected on said ski bottom surface.

8. The method as defined in claim 6, wherein said zones of vibratory motion are such that the ski is substantially always in supporting relationship with at least two zones of vibratory motion.

9. The method as defined in claim 6, wherein said zones of motion are produced by coupling said elecromechanical vibratory mechanism means to the upper surface of the ski.

10. A method as defined in claim 6, wherein said ski is relatively thin as compared to its width or length and defines a planar bottom surface containing a plurality of said zones of vibratory motion.

11. A method as defined in claim 6, wherein said zones of motion are produced by positioning said electromechanical vibratory mechanism means between the upper surface and said bottom surface of the ski.

12. A method as defined in claim 1, and further including the step of carrying by the skier of an electronic generator and battery for powering said electromechanical vibratory mechanism means.

13. A method as defined in claim 12, and further including the step of recharging said battery from time to time.

14. A ski system, comprising A. a ski having a substantially continuous planar bottom surface capable of transmiting ultrasonic vibrations and capable of supporting a skier wearing them on a ski supporting surface,

B. electromechanical vibratory mechanism means coupled to said ski for transmitting mechanical vibrations on said ski bottom surface,

C. generator means for activating said electromechanical vibratory mechanism means, and

D. said electromechanical vibratory mechanism means producing said vibration at high frequency and low amplitude having a component substantially normal to said ski supporting surface, said mechanical vibrations producing peak accelerations of the order of at least 1,000g, whereby the coefficient of friction between said ski bottom and the ski supporting surface is quantitatively reduced.

15. A system as defined in claim 14, wherein said ultrasonic vibration effects elastic vibration of said bottom surface at a frequency of at least 10,000 cycles per second.

16. The system as defined in claim 14, wherein said high frequency vibration is in the range of 10,000 to 1,000,000 cycles per second.

17. A system as defined in claim 14, wherein said vibration generating means includes an ultrasonic motor connected to said vibration generator.

18. A system as defined in claim 17, wherein said vibration generator is adapted to be carried by the user.

19. A system as defined in claim 18, wherein said generator is battery powered.

20. A system as defined in claim 17, wherein said ultrasonic motor is coupled to the upper surface of the ski.

21. A system as defined in claim 17, wherein said ultrasonic motor is contained within said ski.

22. A system as defined in claim 14, and further including means for controlling the coefficient of friction between the ski and ski supporting surface by varying the amplitude of vibration.

23. A system as defined in claim 14, and further including retaining means for connecting the ski to the boot of the skier.

24. A system as defined in claim 14, wherein said vibration produces spaced apart zones of vibratory motion along said bottom surface.

25. A ski system, comprising A. a ski having a substantially continuous planar bottom surface capable of transmiting ultrasonic vibrations and capable of supporting a skier wearing them,

B. a plurality of spaced apart electromechanical vibratory mechanism means coupled to said ski for transmitting mechanical vibrations on said ski bottom surface, and including an ultrasonic motor,

C. battery powered generator means for activating said ultrasonic motor, and

D. said electromechanical vibratory mechanism means producing said vibration at high frequency and low amplitude in spaced apart zones of vibratory motion having a component substantially normal to said ski supporting surface, said mechanical vibrations producing peak accelerations of the order of at least 1,000g and at a frequency in the range of 10,000 to 1,000,000 cycles per second, whereby the coefiicient of friction between said ski bottom and the ski supporting surface is quantitatively reduced.

26. A system as defined in claim 25, wherein said ski is relatively thin as compared to its width or length and defines a planar ski bottom surface containing a plurality of said zones of vibratory motion.

27. A ski, comprising A. a planar bottom surface capable of transmitting ultrasonic vibrations and spaced upper surface capable of supporting a skier thereon,

B. a plurality of spaced apart electromechanical vibratory mechanism means coupled to said ski for transmitting mechanical vibrations on said ski bottom surface,

C. generator means for activating said electromechanical vibratory mechanism means positioned on said ski, and

D. said electromechanical vibratory mechanism means producing said vibration at high frequency and low amplitude having a component substantially normal to said ski supporting surface, said mechanical vibrations producing peak acceleramechanical vibratory mechanism means is in the form of a transducer coupled to the upper surface of the ski.

31. A ski as defined in claim 27, wherein said electromechanical vibratory mechanism means is in the form of a transducer contained within said ski.

32. A ski as defined in claim 27, wherein said ultrasonic vibration effects elastic vibration of said bottom surface at a frequency of at least 10,000 cycles per second. 

1. The method of skiing on a ski supporting surface comprising the steps of A. providing a ski having a substantially continuous planar, bottom surface capable of transmitting ultrasonic vibrations and capable of supporting a skier wearing them, B. coupling electromechanical vibratory mechanism means to said ski for transmitting mechanical vibrations on said ski bottom surface, and C. activating said electromechanical vibratory mechanism means to produce said vibration at high frequency and low amplitude having a component substantially normal to said ski bottom surface, and with peak accelerations of the order of at least 1,000g, whereby the coefficient of friction between said ski bottom surface and the ski supporting surface is quantitatively reduced.
 2. The method as defined in claim 1, wherein said ultrasonic vibration effects elastic vibration of said ski bottom surface at a frequency of at least 10,000 cycles per second.
 3. The method as defined in claim 1, wherein said high frequency vibration is in the range of 10,000 to 1,000,000 cycles per second.
 4. The method as defined in claim 1, and further including the step of controlling the coefficient of sliding friction between the ski and supporting surface by varying the amplitude of vibration of said ski bottom surface.
 5. A method as defined in claim 1, and further including the step of controlling the coefficient of friction between the skis and ski-slope by varying the frequency of vibration of said ski bottom surface.
 6. The method as defined in claim 1, wherein said vibration produces zones of vibratory motion along said bottom surface.
 7. The method as defined in claim 6, wherein said zones of vibratory motion are randomly selected on said ski bottom surface.
 8. The method as defined in claim 6, wherein said zones of vibratory motion are such that the ski is substantially always in supporting relationship with at least two zones of vibratory motion.
 9. The method as defined in claim 6, wherein said zones of motion are produced by coupling said elecro-mechanical vibratory mechanism means to the upper surface of the ski.
 10. A method as defined in claim 6, wherein said ski is relatively thin as compared to its width or length and defines a planar bottom surface containing a plurality of said zones of vibratory motion.
 11. A method as defined in claim 6, wherein said zones of motion are produced by positioning said electromechanical vibratory mechanism means between the upper surface and said bottom surface of the ski.
 12. A method as defined in claim 1, and further including the step of carrying by the skier of an electronic generator and battery for powering said electromechanical vibratory mechanism means.
 13. A method as defined in claim 12, and further including the step of recharging said battery from time to time.
 14. A ski system, comprising A. a ski having a substantially continuous planar bottom surface capable of transmiting ultrasonic vibrations and capable of supporting a skier wearing them on a ski supporting surface, B. electromechanical vibratory mechanism means coupled to said ski for transmitting mechanical vibrations on said ski bottom surface, C. generator means for activating said electromechanical vibratory mechanism means, and D. said electromechanical vibratory mechanism means producing said vibration at high frequency and low amplitude having a component substantially normal to said ski supporting surface, said mechanical vibrations producing peak accelerations of the order of at least 1,000g, whereby the coefficient of friction between said ski bottom and the ski supporting surface is quantitatively reduced.
 15. A system as defined in claim 14, wherein said ultrasonic vibration effects elastic vibration of said bottom surface at a frequency of at least 10,000 cycles per second.
 16. The system as defined in claim 14, wherein said high frequency vibration is in the range of 10,000 to 1,000,000 cycles per second.
 17. A system as defined in claim 14, wherein said vibration generating means includes an ultrasonic motor connected to said vibration generator.
 18. A system as defined in claim 17, wherein said vibration generator is adapted to be carried by the user.
 19. A system as defined in claim 18, wherein said generator is battery powered.
 20. A system as defined in claim 17, wherein said ultrasonic motor is coupled to the upper surface of the ski.
 21. A system as defined in claim 17, wherein said ultrasonic motor is contained within said ski.
 22. A system as defined in claim 14, and further including means for controlling the coefficient of friction between the ski and ski supporting surface by varying the amplitude of vibration.
 23. A system as defined in claim 14, and further including retaining means for connecting the ski to the boot of the skier.
 24. A system as defined in claim 14, wherein said vibration produces spaced apart zones of vibratory motion along said bottom surface.
 25. A ski system, comprising A. a ski having a substantially continuous planar bottom surface capable of transmiting ultrasonic vibrations and capable of supporting a skier wearing them, B. a plurality of spaced apart electromechanical vibratory mechanism means coupled to said ski for transmitting mechanical vibrations on said ski bottom surface, and including an ultrasonic motor, C. battery powered generator means for activating said ultrasonic motor, and D. said electromechanical vibratory mechanism means producing said vibration at high frequency and low amplitude in spaced apart zones of vibratory motion having a component substantially normal to said ski supporting surface, said mechanical vibrations producing peak accelerations of the order of at least 1,000g and at a frequency in the range of 10,000 to 1,000,000 cycles per second, whereby the coefficient of friction between said ski bottom and the ski supporting surface is quantitatively reduced.
 26. A system as defined in claim 25, wherein said ski is relatively thin as compared to its width or length and defines a planar ski bottom surface containing a plurality of said zones of vibratory motion.
 27. A ski, comprising A. a planar bottom surface capable of transmitting ultrasonic vibrations and spaced upper surface capable of supporting a skier thereon, B. a plurality of spaced apart electromechanical vibratory mechanism means coupled to said ski for transmitting mechanical vibrations on said ski bottom surface, C. generator means for activating said electromechanical vibratory mechanism means positioned on said ski, and D. said electromechanical vibratory mechanism means producing said vibration at high frequency and low amplitude having a component substantially normal to said ski supporting surface, said mechanical vibrations producing peak accelerations of the order of at least 1,000g, whereby the coefficient of friction between said ski bottom and the ski supporting surface is quantitatively reduced.
 28. A ski as defined in claim 27, wherein said generator is battery powered.
 29. A ski as defined in claim 28, and further including an electrical outlet on said ski connected to said battery for recharging same.
 30. A ski as defined in claim 27, wherein said electromechanical vibratory mechanism means is in the form of a transducer coupled to the upper surface Of the ski.
 31. A ski as defined in claim 27, wherein said electromechanical vibratory mechanism means is in the form of a transducer contained within said ski.
 32. A ski as defined in claim 27, wherein said ultrasonic vibration effects elastic vibration of said bottom surface at a frequency of at least 10,000 cycles per second. 